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pps: add parallel port PPS signal generator
Add PPS signal generator which utilizes STROBE pin of a parallel port to send PPS signals. It uses parport abstraction layer and hrtimers to precisely control the signal. Signed-off-by: Alexander Gordeev <lasaine@lvk.cs.msu.su> Cc: Rodolfo Giometti <giometti@linux.it> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -2,16 +2,12 @@
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# PPS generators configuration
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#
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if PPS
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comment "PPS generators support"
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config PPS_GENERATOR_PARPORT
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tristate "Parallel port PPS signal generator"
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depends on PARPORT != n && GENERIC_TIME
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depends on PARPORT
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help
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If you say yes here you get support for a PPS signal generator which
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utilizes STROBE pin of a parallel port to send PPS signals. It uses
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parport abstraction layer and hrtimers to precisely control the signal.
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endif
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@ -76,8 +76,15 @@ static enum hrtimer_restart hrtimer_event(struct hrtimer *timer)
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long lim, delta;
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unsigned long flags;
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/* NB: approx time with blocked interrupts =
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send_delay + 3 * SAFETY_INTERVAL */
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/* We have to disable interrupts here. The idea is to prevent
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* other interrupts on the same processor to introduce random
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* lags while polling the clock. getnstimeofday() takes <1us on
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* most machines while other interrupt handlers can take much
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* more potentially.
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*
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* NB: approx time with blocked interrupts =
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* send_delay + 3 * SAFETY_INTERVAL
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*/
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local_irq_save(flags);
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/* first of all we get the time stamp... */
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